High quality thin oxide films of metals, such as Ta2O5 layers, deposited on semiconductor wafers have recently gained interest for use in memories (e.g., dynamic random access memory (DRAM) devices, static random access memory (SRAM) devices, and ferroelectric memory (FERAM) devices). These materials, particularly Ta2O5, have very high dielectric constants and therefore are attractive as capacitor dielectrics and gate dielectrics.
Suitable metal oxides are typically delivered to a substrate in the vapor phase. Vapor deposition processes, which includes chemical vapor deposition (CVD) and atomic layer deposition (ALD), are very appealing as they provide for excellent control of dielectric uniformity and thickness on a substrate.
Many oxides are difficult to deliver using vapor deposition technology. Many precursors are sensitive to thermal decomposition. Also, many precursors have vapor pressures that are too low for effective vapor deposition. For example, molecules containing certain low-valent metals tend to aggregate, which causes poor volatility. Many other precursors that have sufficient volatility, such as tantalum pentaethoxide, require rather high temperatures to attain significant vapor pressure. This can present certain technical difficulties with delivery of the vapor to the deposition chamber. The modified precursor, tantalum tetraethoxydimethylaminoethoxide, has significantly higher vapor pressure; however, the presence of nitrogen may be a problem with migration into transistors.
Thus, there is a continuing need for methods and materials for the deposition of tantalum oxide films using vapor deposition processes on substrates, particularly semiconductor structures such as random access memory devices.